If it helps any, I used tech grade acids routinely-----the sole exception being I used reagent HCl for the final wash of gold that was refined a second time. I had no problems with purity, and achieved perfectly acceptable results on my gold for many years, refining commercially.
Judge for yourself. Here's a picture taken of the last gold I refined before selling my small business. It was processed exactly as I described, including the use of tap water. No flux was used in melting the gold aside from a thin coat on the dish, and the gold did not require pickling to improve appearance. There were no oxides.
It's more likely your end results will be influenced far more by the way you handle the gold than any possible effects you may suffer from your choice of acids.
Harold
